In relatively small turbine engines in airborne environments, fuel flows at high altitudes, particularly during the starting of the turbine engine, are frequently quite low. Consequently, so-called "start injectors" requiring high fuel pressures are commonly used to achieve pressure atomization of the fuel sufficient to initiate ignition and generate sufficient hot gas as to accelerate the turbine wheel of the engine toward a self-sustaining speed. Once that has occurred, the start injector or injectors are de-energized and drop out of the system, fuel necessary to maintain and further accelerate the turbine wheel being provided through so-called "main" injectors.
This mode of operation requires that the start injector or injectors be purged of residual fuel once they are deactivated. If that is not done, the heat within the engine combustor will shortly cause pyrolysis of residual fuel in the injector which will result in the formation of gummy, coke-like products which plug or partially plug the start injectors. Consequently, such a system requires control components, including valves for coupling or decoupling start injectors from the system as well as some sort of means that provide for purging of the start fuel injector or injectors. These components add expense to the construction of the fuel system as well as an element of increased complexity which, in turn, may lower reliability.
In the above-identified, co-pending application, as well as its parent application, there are disclosed unique fuel injectors for use in turbine engines that achieve good atomization of fuel at low flow rates by air blast atomization as opposed to pressure atomization. The present invention seeks to make use of such injectors in a new and improved fuel system that is simple in construction and which, therefore, may be economically fabricated and which has improved reliability.